1. Technical Field
The present invention generally relates to a transportation apparatus for transporting a transportation target medium, a recording apparatus that is provided with the transportation apparatus for transporting a transportation target medium, and a control method for controlling the transportation apparatus for transporting a transportation target medium. More particularly, the present invention relates to a transportation apparatus for transporting a sheet-type transportation target medium while holding it between a pair of pinching rollers thereof during transportation. The present invention further relates to a recording apparatus that is provided with such a transportation apparatus, and a control method for controlling such a transportation apparatus.
2. Related Art
In the related technical fields of the invention, transportation units are built in a variety of apparatuses/equipment such as a recording apparatus, a facsimile machine, and a copying machine, though not limited thereto, for the functional purpose of transporting sheet-shaped transportation target media, sheet-shaped recording target media, or the like. As an example of these transportation units, one known in the art is configured to transport a transportation target medium while holding it between a pair of pinching rollers of the transportation apparatus during transportation, at least one of which is/are driven in a rotational manner. Such a type of transportation unit has a driving roller that is operated rotationally (i.e., rotates actively) and a driven roller that follows the rotary movement of the driving roller (i.e., rotates passively). In such a configuration, the driven roller applies a pressing force onto a transportation target medium toward the driving roller. As the driving roller rotates, the transportation target medium is transported while being pinched therebetween.
The patent document JP-A-2002-128314 discloses a paper transportation apparatus that has a driving roller and a driven roller that is urged toward the driving roller. The paper transportation apparatus described in JP-A-2002-128314 transports a sheet of paper in accordance with the rotation of the driving roller. During transportation, the sheet of paper is supported between the driving roller and the driven roller. In addition to these rollers, the paper transportation apparatus according to JP-A-2002-128314 is further provided with an urging member that urges the driven roller toward the driving roller and an arm member that allows the driven roller to move apart from the driving roller against the urging force applied thereto by the urging member. With such a configuration, it is possible to remove, if there occurs any paper jam malfunction between the driving roller and the driven roller, a jammed paper by releasing the pinching force exerted by the driven roller without causing any adverse mechanical stress on each of these rollers.
The patent document JP-A-2002-192782 teaches a configuration in which, at an ejection unit of a recording apparatus that is a kind of transportation apparatus, a holder that is configured to be capable of moving in a rotating direction (i.e., drawing/tracing an arc) supports an ejection driven roller. With such a configuration, it is possible to prevent a recording target material/medium from being damaged by moving the ejection driven roller apart from an ejection driving roller. As described above, some of transportation apparatuses that have a pair of pinching rollers provided for transportation of a transportation target medium allow a driving roller and a driven roller to become distanced from (i.e., not in contact with) each other when there is no transportation target medium that is now being transported.
A related-art transportation unit such as one described above transports various kinds of sheet-type recording target media that vary in terms of thickness from one to another. Nowadays, it is not infrequent that, in addition to a sheet of recording paper having a thickness of less than 1 mm, which is flexible, a sheet of cardboard paper, information recording medium, printed wiring board, and the like having a thickness of 3 mm of greater is fed as a target of transportation. In a related-art application where a transportation unit having the roller mechanism described above transports such a thick-type recording target medium, as a pre-transportation step, a driven roller is temporarily moved apart from a driving roller so as to form a sufficiently large clearance therebetween; and thereafter, the thick recording target medium is fed therebetween. With such a procedure/configuration, the related-art transportation unit described above ensures the smooth feeding of the recording target medium. In addition, the above-described procedure/configuration makes it possible to reduce any undesirable mechanical stress applied to constituent members that make up the transportation unit.
In the roller configuration of the above-described transportation apparatus that has a combination of the driving roller and the driven roller, it is preferable that the driven roller can rotate smoothly as the driving roller rotates. In order to ensure the smooth rotation of the driven roller, an urging force is not directly applied to the driven roller but indirectly thereto via a driven roller holder. The driven roller holder supports the driven roller in such a manner that the driven roller can rotate freely. For the same reason, when the driven roller is moved apart from the driving roller, it is done so by means of the driven roller holder.
When the driven roller holder is turned so as to move the driven roller apart from the driving roller, the mechanical stress due to the urging force is applied to the driven roller holder. Disadvantageously, plastic deformation could occur on the driven roller holder, most of which is made of a resin material, if the driven roller continues to be distanced apart from the driving roller for a long time period. As a result of the plastic deformation of the driven roller holder, a gap between the driving roller and the driven roller decreases. Eventually, the gap therebetween decreases into an insufficient level. If the gap between the driving roller and the driven roller is set at a larger value in anticipation of such plastic deformation of the driven roller holder, a wide open space is required in the periphery of the driven roller holder because the moving vector amount of the driven roller becomes larger. For this reason, disadvantageously, the size of a transportation apparatus increases. On the other hand, an expensive deformation-free material must be used in order to avoid the driven roller holder from becoming deformed. Or, it is necessary to increase the size of the driven roller holder itself for the prevention of plastic deformation thereof, which results in an undesirable increase in the size of the transportation apparatus.